Semiconductor device

ABSTRACT

An object of the present invention is to shorten time required for detecting disconnection in an input terminal of an A/D conversion circuit. A semiconductor device includes a first input channel that couples a first input terminal and an A/D conversion unit to each other, a second input channel that couples a second input terminal and the A/D conversion unit to each other, and a control circuit unit that separates the second input channel from the second input terminal and the A/D conversion unit to charge or discharge the second input channel when a signal input into the first input terminal is sampled by the A/D conversion unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 15/265,048, filed Sep. 14, 2016, which claims the benefit of Japanese Patent Application No. 2015-188108 filed on Sep. 25, 2015 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND

The disclosure relates to a semiconductor device, and can be applied to a semiconductor device including, for example, an A/D conversion circuit.

In the case where a signal from a sensor is fetched to perform a process in accordance with the status of the signal in a semiconductor device such as a microcomputer, an A/D conversion circuit that converts the analog signal from the sensor to a digital signal available in a control circuit is used. A safety function of automatically avoiding a situation related to human life is mounted in automobiles and the like. Such a function is realized by a semiconductor device to which various sensors are coupled. If disconnection occurs in an input signal line of the A/D conversion circuit in such a semiconductor device, a signal from an important sensor is not input, and the semiconductor device cannot detect occurrence of an abnormal situation, resulting in a serious problem that the safety function is not executed when needed. In order to prevent such false determination of the semiconductor device, a technique of reliably detecting the disconnection has been proposed (for example, US Patent Application Publication No. 2010/0245141).

SUMMARY

US Patent Application Publication No. 2010/0245141 describes that disconnection can be detected without being affected by wiring capacitance outside a microcomputer of an input signal unit for A/D conversion. However, electric charges are charged to or discharged from a sample hold capacitor to detect the disconnection, and further A/D conversion is performed in one terminal, at least, twice. Accordingly, time more than twice the normal A/D conversion is required. The other objects and novel features will become apparent from the description of the specification and the accompanying drawings.

The following is a representative summary of the disclosure. Namely, a semiconductor device includes an A/D conversion circuit having a mechanism of charging or discharging, during A/D conversion, parasitic capacitance to/from a terminal in which A/D conversion is not performed.

According to the above-described semiconductor device, it is possible to shorten time required for detecting disconnection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram for showing a configuration of a semiconductor device according to an example;

FIG. 2 is a block diagram for showing a configuration of an A/D conversion circuit of FIG. 1;

FIG. 3 is a circuit diagram for showing a configuration of an input unit of FIG. 2;

FIG. 4 is a timing diagram of the A/D conversion circuit of FIG. 2;

FIG. 5 is a diagram for explaining switch control of a selected input channel of FIG. 3;

FIG. 6A is a diagram for explaining switch control of an unselected input channel (period CD) of FIG. 3;

FIG. 6B is a diagram for explaining switch control of the unselected input channel (period PCD) of FIG. 3;

FIG. 7 is a block diagram for showing a configuration of an A/D conversion circuit according to a first modified example;

FIG. 8 is a circuit diagram for showing a configuration of an input unit of FIG. 7;

FIG. 9 is a circuit diagram for showing a configuration of a signal transmission unit of FIG. 8;

FIG. 10 is a timing diagram of the A/D conversion circuit of FIG. 7;

FIG. 11A is a diagram for explaining switch control of a selected input channel (period A) of FIG. 9;

FIG. 11B is a diagram for explaining switch control of the selected input channel (period B) of FIG. 9;

FIG. 12A is a diagram for explaining switch control of an unselected input channel (period CD) of FIG. 9;

FIG. 12B is a diagram for explaining switch control of the unselected input channel (period PCD) of FIG. 9;

FIG. 13 is a block diagram for showing a configuration of an A/D conversion circuit according to a second modified example;

FIG. 14 is a circuit diagram for showing a configuration of an input unit of FIG. 13;

FIG. 15 is a circuit diagram for showing a configuration of a signal transmission unit of FIG. 14;

FIG. 16 is a timing diagram of the A/D conversion circuit of FIG. 13;

FIG. 17A is a diagram for explaining switch control of a selected input channel (period A) of FIG. 15;

FIG. 17B is a diagram for explaining switch control of the selected input channel (period B) of FIG. 15;

FIG. 17C is a diagram for explaining switch control of the selected input channel (period PA) of FIG. 15;

FIG. 18A is a diagram for explaining switch control of an unselected input channel (period CD) of FIG. 15;

FIG. 18B is a diagram for explaining switch control of the unselected input channel (period PCD) of FIG. 15;

FIG. 19 is a block diagram for showing a configuration of an A/D conversion circuit according to a third modified example;

FIG. 20 is a circuit diagram for showing a configuration of an input unit of FIG. 19;

FIG. 21 is a circuit diagram for showing a configuration of a signal transmission unit of FIG. 20;

FIG. 22 is a timing diagram of the A/D conversion circuit of FIG. 19;

FIG. 23A is a diagram for explaining switch control of a selected input channel (period A) of FIG. 21;

FIG. 23B is a diagram for explaining switch control of the selected input channel (period B) of FIG. 21;

FIG. 24A is a diagram for explaining switch control of an unselected input channel (period CD) of FIG. 21;

FIG. 24B is a diagram for explaining switch control of the unselected input channel (period PCD) of FIG. 21;

FIG. 25 is a block diagram for showing a configuration of a motor control system according to a first application;

FIG. 26 is a block diagram for showing a configuration of an air-bag system according to a second application; and

FIG. 27 is a block diagram for showing a configuration of a semiconductor device according to an embodiment.

DETAILED DESCRIPTION

Hereinafter, an embodiment, an example, modified examples, and applications will be described using the drawings. However, the same signs are given to the same constitutional elements in the following description, and repeated explanations will be omitted in some cases.

Embodiment

A configuration of a semiconductor device according to an embodiment will be described using FIG. 27. The semiconductor device according to the embodiment includes a first input terminal (CH1), a second input terminal (CH2), an A/D conversion unit (ADC) having a sample hold circuit (S/H), a first input channel (CHN1) that couples the first input terminal (CH1) to the A/D conversion unit (ADC), a second input channel (CHN2) that couples the second input terminal (CH2) to the A/D conversion unit (ADC), and a control unit (CNT). When a signal input into the first input terminal (CH1) is sampled by the sample hold circuit (S/H), the control unit (CNT) separates the second input channel (CHN2) from the second input terminal (CH2) and the A/D conversion unit (ADC) to charge or discharge the second input channel (CHN2).

According to the embodiment, since an unselected input channel is charged or discharged, disconnection can be detected by A/D conversion when the input channel is selected. Further, if disconnection is not detected, the A/D conversion result is obtained by normal A/D conversion. Thus, it is not necessary to perform A/D conversion for detecting disconnection that is different from normal A/D conversion. In other words, disconnection can be detected during normal A/D conversion.

EXAMPLE

A configuration of a semiconductor device according to an example will be described using FIGS. 1 to 3. As shown in FIG. 1, a microcontroller (MCU) 1 that is a semiconductor device includes, on a semiconductor substrate, an A/D conversion circuit (ADC) 11, an internal bus (BUS) 12, an electrically-erasable or electrically-writable nonvolatile memory (NVM) 13 such as a flash memory, and a central processing unit (CPU) 14. On the basis of a program read from the nonvolatile memory 13 through the internal bus (BUS) 12, the CPU 14 controls the A/D conversion circuit 11 through the internal bus 12 to read an A/D conversion result through the internal bus 12. A signal output from a signal generation source such as a sensor is input into input terminals CH1 to CHn coupled to the A/D conversion circuit 11.

As shown in FIG. 2, the A/D conversion circuit 11 includes an input signal selection unit 22, an input unit 20, an A/D conversion unit 26, a control unit 27, and a comparison determination unit 29. The A/D conversion circuit 11 further includes an A/D conversion result storing unit 15, an upper/lower limit determination result storing unit 16, and an upper-limit/lower-limit value storing unit 17 that are coupled to the internal bus 12 through the control unit 27 and are configured using memories and registers from/into which data can be read and written by the CPU 14.

The input signal selection unit 22 allows input signal selection switches F1 to Fn to selectively output signals input through the input terminals CH1 to CHn to input signal lines FT1 to FTn. The input signal lines FT1 to FTn are coupled to the input unit 20. The input signal selection unit 22 needs to select a target input terminal when A/D conversion is performed. Thus, the number of input signal selection switches F1 to Fn is the same as that of input terminals CH1 to CHn. These input signal selection switches F1 to Fn are controlled by control signals (CF1 to CFn) from the control unit 27.

As shown in FIG. 3, the input unit 20 includes a charge unit 21, a parasitic capacitance unit 23, a signal transmission unit STU, and a discharge unit 28. In the charge unit 21, the input signal lines FT1 to FTn are coupled to a power supply line (Vdd) through charge control switches M1 to Mn, and an output signal line CT is coupled to the power supply line (Vdd) through a charge switch E. Opening/closing of the charge control switches M1 to Mn and the charge switch E is controlled by control signals (CM1 to CMn and CE) output from the control unit 27. In the discharge unit 28, the input signal lines FT1 to FTn are coupled to a grounding wire through discharge control switches N1 to Nn, and the output signal line CT is coupled to the grounding wire through a discharge switch D. Opening/closing of the discharge control switches N1 to Nn and the discharge switch D is controlled by control signals (CN1 to CNn and CD) output from the control unit 27. The parasitic capacitance unit 23 includes capacitors PS11 to PS1 n that are parasitic capacitances between the input signal lines FT1 to FTn and the grounding wire.

The signal transmission unit STU includes a switch unit 24 and a parasitic capacitance unit 25. In the switch unit 24, the input signal lines FT1 to FTn are coupled to the output signal line CT through switches G1 to Gn. Opening/closing of the switches G1 to Gn is controlled by control signals (CG1 to CGn) output from the control unit 27. The parasitic capacitance unit 25 includes a capacitor PS2 that is a parasitic capacitance between the output signal line CT and the grounding wire.

Routes from the input terminals CH1 to CHn to the output signal line CT through the input signal selection switches F1 to Fn, the input signal lines FT1 to FTn, and the switches G1 to Gn are referred to as a first input channel to an n-th input channel, respectively. When the n-th input channel is selected, an output signal of a signal generation source coupled to the input terminal CHn is fetched to the A/D conversion unit 26. Outputs of the first input channel to the n-th input channel are bound to the output signal line CT, and thus only one of the first input channel to the n-th input channel is selected.

As shown in FIG. 2, the A/D conversion unit 26 has a sample hold (S/H) circuit unit C1 that holds electric charges of the output signal line CT and an A/D conversion mechanism C2 that performs A/D conversion for the held electric charges, and outputs an A/D conversion result (DT) to the comparison determination unit 29. The comparison determination unit 29 compares the A/D conversion result (DT) output from the A/D conversion unit 26 with upper/lower limit data (IT) output from the upper-limit/lower-limit value storing unit 17, and stores the result into the upper/lower limit determination result storing unit 16 as an upper/lower limit determination result (HT). When the comparison result is determined as disconnection, the result is notified to the CPU 14 as an interruption request signal (JT). Further, the comparison determination unit 29 stores the A/D conversion result (DT) into the A/D conversion result storing unit 15.

An operation of the A/D conversion circuit of FIG. 2 will be described using FIGS. 4, 5, 6A, and 6B. The switching control of the A/D conversion circuit differs depending on the input terminal (selected input channel) in which A/D conversion is performed and the input terminal (unselected input channel) in which A/D conversion is not performed. The input channels are the first input channel to the n-th input channel, but the n-th input channel will be described below as a representative channel.

When a signal of the input terminal CHn is A/D converted, the control unit 27 puts the input signal selection switch Fn in a conductive state, and puts the input signal selection switches other than the input signal selection switch Fn in a non-conductive state.

In a period CD of FIG. 4, in order to suppress the influence of the electric charges when A/D conversion is performed at a different terminal before the electric charges of the signal generation source are charged to the S/H circuit unit C1, the control unit 27 puts the discharge switch D in a conductive state before A/D conversion to discharge the electric charges from the S/H circuit unit C1 and the parasitic capacitance unit 25 as shown in FIG. 6A. The control unit 27 puts the switches other than the discharge switch D in a non-conductive state. A case in which the electric charges are discharged will be mainly described below. However, the same control is performed even in the case where the electric charges are charged. The charging or discharging can be selected on an input channel basis. The period CD corresponds to the charging or discharging period of the S/H circuit unit C1.

In a period B of FIG. 4, after the electric charges are discharged from the S/H circuit unit C1, the control unit 27 charges the electric charges to the S/H circuit unit C1 by putting the switch Gn in a conductive state as shown in FIG. 5. The control unit 27 puts each switch of the charge unit 21 and the discharge unit 28 in a non-conductive state. The period B corresponds to the sampling period of the S/H circuit unit C1 (period S).

In a period C of FIG. 4, after the charging of the electric charges of the signal generation source to the S/H circuit unit C1 is completed, the control unit 27 performs A/D conversion by putting the switch Gn in a non-conductive state. The period C corresponds to the conversion period of the A/D conversion unit 26.

In the case where a signal of the input terminal CHn is not A/D converted, when the charging of the electric charges to the S/H circuit unit C1 is determined on the basis of the lower limit to detect disconnection, the control unit 27 puts the input signal selection switch Fn in a non-conductive state, puts the switch Gn in a non-conductive state, and puts the discharge control switch Nn in a conductive state to discharge the electric charges charged to the parasitic capacitance unit 23 (capacitor PS1 n) in a period PCD of FIG. 4 as shown in FIG. 6B. Namely, the control unit 27 puts the switches other than the discharge control switch Nn in a non-conductive state. The period Pm corresponds to the discharging or charging period of the input signal line FTn. When the input terminal CHn is in a disconnection state, the electric charges are discharged from the parasitic capacitance unit 23 (capacitor PS1 n) to discharge the electric charges from the input signal line FTn to the A/D conversion unit 26 when A/D conversion is performed. Accordingly, the comparison determination unit 29 determines that the A/D conversion result becomes around 0V, and the disconnection state is detected.

In the case where a signal of the input terminal CHn is not A/D converted, when the charging of the electric charges to the S/H circuit unit C1 is determined on the basis of the upper limit to detect disconnection, the switch Gn is put in a non-conductive state, and the charge control switch Mn is put in a conductive state to charge the electric charges to the parasitic capacitance unit 23 in the period PCD of FIG. 4. Namely, the control unit 27 puts the switches other than the charge control switch Mn in a non-conductive state. When the input terminal CHn is in a disconnection state, the electric charges are charged to the parasitic capacitance unit 23 to charge the electric charges from the input signal line FTn to the A/D conversion unit 26 when A/D conversion is performed. Accordingly, the comparison determination unit 29 determines that the A/D conversion result becomes around a power supply voltage (for example, 5V), and the disconnection state is detected.

The A/D conversion result of 0V or 5V relative to a sensor input voltage (for example, 0.15V to 4.85V) can be obtained. Thus, the disconnection detection is determined by setting, for example, the lower-limit value data stored in the upper-limit/lower-limit value storing unit to 0.1V between 0 and 0.15V and by setting the upper-limit value data to 4.9V between 4.85 and 5V. When an input from each selected input channel has a normal value (for example, 3V), the electric charges corresponding to 3V are accumulated in the S/H circuit unit C1 to perform A/D conversion, and the A/D conversion result of 3V can be obtained. However, when there is a disconnection abnormality in an input terminal, no electric charges are accumulated in the S/H circuit unit C1. Thus, the electric charges accumulated in the S/H circuit unit C1 remain in the state (0V or 5V) in which the S/H circuit unit C1 is initialized. If A/D conversion is performed in this case, the conversion result of 0V or 5V can be obtained, and the comparison determination unit 29 can determine as disconnection. It should be noted that the upper/lower limit data (IT) is set in accordance with the input voltage range of the sensor, and is not limited to the above-described values.

In each input channel, the period CD, the period B, and the period PCD are periodically repeated in order. The period CD and the period B of one input channel are performed in parallel with the period PCD of a different input channel. In other words, A/D conversion of a signal input into one input channel is performed in parallel with the charging or discharging of a different input channel.

According to the example, a mechanism of charging or discharging the parasitic capacitance during A/D conversion is added to the terminal (input channel) in which A/D conversion is not performed, and thus disconnection can be detected by one A/D conversion. Further, disconnection can be detected during normal A/D conversion.

It should be noted that when the control signal for a switch is of a high level, the switch is put in a conductive state. When the control signal for a switch is of a low level, the switch is put in a non-conductive state. The discharge switch D and the charge switch E are controlled on an input channel basis, and are not simultaneously put in a conductive state. The charge control switch Mn is valid when the charge switch E is controlled, and the discharge control switch Nn is valid when the discharge switch D is controlled. When the switches are invalid, the switches are always put in a non-conductive state. The same applies to the following first to third modified examples.

First Modified Example

A configuration of an A/D conversion circuit according to a first modified example of the example will be described using FIGS. 7 to 9. As shown in FIG. 7, an A/D conversion circuit 11A according to the first modified example has the same configuration as the example except for a signal transmission unit STUA and a control unit 27A. As shown in FIG. 8, an input unit 20A according to the first modified example is obtained by replacing the signal transmission unit STU of FIG. 3 with the signal transmission unit STUA of FIG. 9.

As shown in FIG. 9, the signal transmission unit STUA includes a bypass/amplifying unit 24A and a parasitic capacitance unit 25A. The bypass/amplifying unit 24A includes bypass switches GA1 to GAn that couple input signal lines FT1 to FTn to an output signal line CT not through amplifiers GC1 to GCn, and amplifier switches GB1 to GBn that couple the input signal lines FT1 to FTn to the output signal line CT through the amplifiers GC1 to GCn. Opening/closing of the bypass switches GA1 to GAn and the amplifier switches GB1 to GBn is controlled by control signals (CGA1 to CGAn and CGB1 to CGBn) output from the control unit 27A. The parasitic capacitance unit 25A includes capacitors PS21 to PS2 n that are parasitic capacitances between the output signal line CT and a grounding wire. A route from the input terminal CHn to the output signal line CT through the input signal selection switch Fn, the input signal line FTn, and the bypass switch GAn (the amplifier GCn and the amplifier switch GBn) is referred to as an n-th input channel.

An operation of the A/D conversion circuit of FIG. 7 will be described using FIGS. 10, 11A, 11B, 12A, and 12B. As similar to the example, the switching control of the A/D conversion circuit differs depending on the input terminal (selected input channel) in which A/D conversion is performed and the input terminal (unselected input channel) in which A/D conversion is not performed. The input channels are the first input channel to the n-th input channel, but the n-th input channel will be described below as a representative channel.

When a signal of the input terminal CHn is A/D converted, the control unit 27A puts the input signal selection switch Fn in a conductive state, and puts the input signal selection switches other than the input signal selection switch Fn in a non-conductive state.

In a period CD of FIG. 10, in order to suppress the influence of the electric charges when A/D conversion is performed at a different terminal before the electric charges of the signal generation source are charged to the S/H circuit unit C1, the control unit 27A puts the discharge switch D in a conductive state before A/D conversion to discharge the electric charges from the S/H circuit unit C1 and the parasitic capacitance unit 25A as shown in FIG. 12A. The control unit 27A puts the switches other than the discharge switch D in a non-conductive state. A case in which the electric charges are discharged will be mainly described below. However, the same control is performed even in the case where the electric charges are charged. The period CD corresponds to the charging or discharging period of the S/H circuit unit C1.

In a period A of FIG. 10, after the electric charges are discharged from the S/H circuit unit C1, the control unit 27A puts the switch GBn in a conductive state to charge the electric charges of the signal generation source to the S/H circuit unit C1 using an output from the amplifier GCn as shown in FIG. 11A. The control unit 27A puts each switch of the charge unit 21 and the discharge unit 28 in a non-conductive state.

In a period B of FIG. 10, in order to improve the accuracy of A/D conversion, the control unit 27A puts the amplifier switch GBn in a non-conductive state, and puts the bypass switch GAn in a conductive state to charge the electric charges of the signal generation source to the S/H circuit unit C1 as shown in FIG. 11B. The control unit 27A puts each switch of the charge unit 21 and the discharge unit 28 in a non-conductive state. The period A and the period B correspond to the sampling period of the S/H circuit unit C1 (period S).

In a period C of FIG. 10, after the charging of the electric charges of the signal generation source to the S/H circuit unit C1 is completed, the control unit 27A performs A/D conversion by putting the bypass switch GAn in a non-conductive state. The period C corresponds to the conversion period of the A/D conversion unit 26.

A case in which a signal of the input terminal CHn is not A/D converted and the charging of the electric charges to the S/H circuit unit C1 is determined on the basis of the lower limit to detect disconnection will be described. The control unit 27A puts the input signal selection switch Fn in a non-conductive state, puts the bypass switch GAn and the amplifier switch GBn in a non-conductive state, and puts the discharge control switch Nn in a conductive state to discharge the electric charges charged to the parasitic capacitance unit 23 (capacitor PS1 n) in a period PCD of FIG. 10 as shown in FIG. 12B. Namely, the control unit 27A puts the switches other than the discharge control switch Nn in a non-conductive state. The period POD corresponds to the discharging or charging period of the input signal line FTn. When the input terminal CHn is in a disconnection state, the electric charges are discharged from the parasitic capacitance unit 23 (capacitor PS1 n) to discharge the electric charges from the input signal line FTn to the A/D conversion unit 26 when A/D conversion is performed. Accordingly, the comparison determination unit 29 determines that the A/D conversion result becomes around 0V, and the disconnection state is detected.

A case in which a signal of the input terminal CHn is not A/D converted and the charging of the electric charges to the S/H circuit unit C1 is determined on the basis of the upper limit to detect disconnection will be described. The control unit 27A puts the bypass switch GAn and the amplifier switch GBn in a non-conductive state, and puts the charge control switch Mn in a conductive state to charge the electric charges to the parasitic capacitance unit 23 (capacitor PS1 n) in the period PCD of FIG. 10. Namely, the control unit 27 puts the switches other than the charge control switch Mn in a non-conductive state. When the input terminal CHn is in a disconnection state, the electric charges are charged to the parasitic capacitance unit 23 to charge the electric charges from the input signal line FTn to the A/D conversion unit 26 when A/D conversion is performed. Accordingly, the comparison determination unit 29 determines that the A/D conversion result becomes around a power supply voltage (for example, 5V), and the disconnection state is detected.

In each input channel, the period CD, the period A, the period B, and the period PCD are periodically repeated in order. The period CD, the period A, and the period B of one input channel are performed in parallel with the period PCD of a different input channel. In other words, A/D conversion of a signal input into one input channel is performed in parallel with the charging or discharging of a different input channel.

According to the first modified example, a disconnection state can be detected as similar to the example even when the amplifier is used for the input unit of the A/D conversion circuit.

Second Modified Example

A configuration of an A/D conversion circuit according to a second modified example of the example will be described using FIGS. 13 to 15. The second modified example is configured in such a manner that an S/H circuit (terminal S/H circuit) provided on an input terminal (input channel) basis and a bypass/terminal S/H circuit unit are added to the signal transmission unit of the first modified example. The bypass/terminal S/H circuit unit includes a switch that selects a route bypassing the terminal S/H circuit and the terminal S/H circuit.

As shown in FIG. 13, an A/D conversion circuit 11B according to the second modified example has the same configuration as the example except for a signal transmission unit STUB and a control unit 27B. As shown in FIG. 14, an input unit 20B according to the second modified example is obtained by replacing the signal transmission unit STU of FIG. 3 with the signal transmission unit STUB of FIG. 15.

As shown in FIG. 15, the signal transmission unit STUB includes a bypass/amplifying unit 24A, a terminal S/H circuit unit 30, and a parasitic capacitance unit 25A. The bypass/terminal S/H circuit unit 30 includes bypass switches HA1 to HAn that couple intermediate signal lines GT1 to GTn of the bypass/amplifying unit 24A to an output signal line CT not through terminal S/H circuits HC1 to HCn, and S/H switches HB1 to HBn that couple the intermediate signal lines GT1 to GTn to the output signal line CT through the terminal S/H circuits HC1 to HCn. Opening/closing of the bypass switches HA1 to HAn and the S/H switches HB1 to HBn is controlled by control signals (CHA1 to CHAn and CHB1 to CHBn) output from the control unit 27B. A route from the input terminal CHn to the output signal line CT through the input signal selection switch Fn, the input signal line FTn, the bypass switch GAn (or the amplifier GCn and the amplifier switch GBn), and the bypass switch HAn (or the terminal S/H circuit HCn and the S/H switch HBn) is referred to as an n-th input channel.

In the second modified example, the bypass/terminal S/H circuit unit is added to the first modified example. However, an additional circuit for discharging the electric charges of the terminal S/H circuit or for charging the electric charges to the terminal S/H circuit is not provided, but switching control is added to charge or discharge the electric charges.

An operation of the A/D conversion circuit of FIG. 13 will be described using FIGS. 16, 17A, 17B, 17C, 18A, and 18B. As similar to the example, the switching control of the A/D conversion circuit differs depending on the input terminal (selected input channel) in which A/D conversion is performed and the input terminal (unselected input channel) in which A/D conversion is not performed. The input channels are the first input channel to the n-th input channel, but the n-th input channel will be described below as a representative channel.

In the switching control, the input signal selection switch Fn of the terminal in which A/D conversion is performed is put in a conductive state, and the control unit 27B charges the electric charges of the signal generation source to the S/H circuit HCn of the terminal S/H circuit unit 30 by controlling the bypass switch GAn and the amplifier switch GBn in a period A and a period B of FIG. 16 as similar to the first modified example as shown in FIGS. 17A and 17B. In this case, the control unit 27B puts each switch of the charge unit 21, the discharge unit 28, and the terminal S/H circuit unit 30 in a non-conductive state. The period A and the period B correspond to the sampling period of the terminal S/H circuit unit 30 unlike the first modified example. After the charging of the electric charges to the terminal S/H circuit unit 30 is completed, the control unit 27B puts the bypass switch GAn and the amplifier switch GBn in a non-conductive state, and allows the terminal S/H circuit HCn to hold the sensor input signal.

In a period CD of FIG. 16, the control unit 27B puts the discharge switch D in a conductive state to discharge the electric charges from the S/H circuit unit C1 and the parasitic capacitance unit 25 before A/D conversion is performed as similar to the example as shown in FIG. 18A. A case in which the electric charges are discharged will be mainly described below. However, the same control is performed even in the case where the electric charges are charged. The period CD corresponds to the charging or discharging period of the S/H circuit unit C1 as similar to the example and the first modified example.

In a period PA of FIG. 16, the control unit 27B puts the discharge switch D in a non-conductive state, puts the input signal selection switch Fn in a non-conductive state, and puts the S/H switch HBn in a conducive state to charge the electric charges of the S/H circuit HCn to the S/H circuit unit C1 as shown in FIG. 17C. Namely, the control unit 27B puts the switches other than the S/H switch HBn in a non-conductive state. The period PA corresponds to the sampling period of the S/H circuit unit C1 (period S).

In a period C of FIG. 16, the control unit 27B puts the S/H switch HBn in a non-conductive state to complete the charging of the electric charges to the S/H circuit unit C1, and A/D conversion is performed by putting the bypass switch HAn in a non-conductive state. The period C corresponds to the conversion period of the A/D conversion unit 26.

A case in which a signal of the input terminal CHn is not A/D converted and the charging of the electric charges to the S/H circuit unit C1 is determined on the basis of the lower limit to detect disconnection will be described. The control unit 27B puts the input signal selection switch Fn in a non-conductive state, puts the amplifier switch GBn in a non-conductive state, puts the bypass switch GAn in a conductive state, and puts the discharge control switch Nn in a conductive state to discharge the electric charges charged to the parasitic capacitance unit 23 (capacitor PS1 n) and the terminal S/H circuit unit 30 in a period PCD of FIG. 16 as shown in FIG. 18B. The control unit 27B puts each switch of the charge unit 21, the discharge switch D, the bypass switch HAn, and the S/H switch HBn in a non-conductive state. The period PCD corresponds to the discharging or charging period of the input signal line FTn as similar to the example and the first modified example. When the input terminal CHn is in a disconnection state, the electric charges are discharged from the parasitic capacitance unit 23 (capacitor PS1 n) and the terminal S/H circuit unit 30 to discharge the electric charges from the input signal line FTn to the A/D conversion unit 26 when A/D conversion is performed. Accordingly, the comparison determination unit 29 determines that the A/D conversion result becomes around 0V, and the disconnection state is detected.

A case in which a signal of the input terminal CHn is not A/D converted and the charging of the electric charges to the S/H circuit unit C1 is determined on the basis of the upper limit to detect disconnection will be described. The control unit 27B puts the amplifier switch GBn in a non-conductive state, puts the bypass switch GAn in a conductive state, and puts the charge control switch Mn in a conductive state to charge the electric charges to the parasitic capacitance unit 23 (capacitor PS1 n) and the terminal S/H circuit unit 30 in the period PCD of FIG. 16. The control unit 27B puts each switch of the discharge unit 28, the charge switch E, the bypass switch HAn, and the S/H switch HBn in a non-conductive state. When the input terminal CHn is in a disconnection state, the electric charges are charged to the parasitic capacitance unit 23 (capacitor PS1 n) and the terminal S/H circuit unit 30 to charge the electric charges from the input signal line FTn to the A/D conversion unit 26 when A/D conversion is performed. Accordingly, the comparison determination unit 29 determines that the A/D conversion result becomes around a power supply voltage (for example, 5V), and the disconnection state is detected.

In each input channel, the period A, the period B, the period CD, the period PA, and the period PCD are periodically repeated in order. Further, the period A and the period B of each input channel are performed in parallel. Thereafter, the periods CD and the periods PA of the first input channel to the n-th input channel are sequentially performed.

In the second modified example, even when the terminal S/H circuit in consideration of motor control is provided in addition to the configuration of the A/D conversion circuit of the first modified example, the electric charges can be discharged or charged from the parasitic capacitance and the S/H circuit unit. Thus, disconnection can be detected during normal A/D conversion as similar to the first modified example. It should be noted that when the terminal S/H function (S/H circuit) is not used, the bypass switch HAn is put in a conductive state and the S/H switch HBn is put in a non-conductive state. Accordingly, an operation similar to the first modified example can be performed.

Third Modified Example

A configuration of an A/D conversion circuit according to a third modified example of the example will be described using FIGS. 19 to 21. The third modified example has a circuit configuration in which the number of amplifying units is reduced from the signal transmission circuit of the first modified example and the amplifier is shared by a plurality of terminals.

As shown in FIG. 19, an A/D conversion circuit 11C according to the third modified example has the same configuration as the example except for a signal transmission unit STUC, a charge unit 21C, a discharge unit 28C, and a control unit 27C. As shown in FIG. 20, the input unit 20C according to the third modified example is obtained by replacing the signal transmission unit STU of FIG. 3 with the signal transmission unit STUC of FIG. 21.

As shown in FIG. 21, the signal transmission unit STUC includes a bypass/amplifying unit 24C and a parasitic capacitance unit 25. The bypass/amplifying unit 24C has bypass switches GA1 to GAn that couple input signal lines FT1 to FTn to an output signal line CT not through a common amplifier IB, amplifier switches GB1 to GBn coupled to the common amplifier IB, a parasitic capacitance unit 31 of an intermediate signal line IT, and a common switch I that couples the output signal line CT to the common amplifier I. The parasitic capacitance unit 31 includes intermediate signal lines IT1 to ITn that couple the amplifier switches GB1 to GBn to the common amplifier IB, and capacitors PS31 to PS3 n that are parasitic capacitances between the amplifier switches GB1 to GBn and a grounding wire. Opening/closing of the bypass switches GA1 to GAn, the amplifier switches GB1 to GBn, and the common switch I are controlled by control signals (CGA1 to CGAn, CGB1 to CGBn, and CI) output from the control unit 27C. A route from the input terminal CHn to the output signal line CT through the input signal selection switch Fn, the input signal line FTn, and the bypass switch GAn (or the amplifier switch GBn, the common amplifier IB, and the common switch I) is referred to as an n-th input channel.

As shown in FIG. 20, a discharge switch DC provided in the discharge unit 28C couples the parasitic capacitance unit 31 to the grounding wire through the intermediate signal line IT. Further, a charge switch EC provided in the charge unit 21C couples the parasitic capacitance unit 31 to a power supply line (Vdd) through the intermediate signal line IT. Here, the intermediate signal line IT is a signal line to which the intermediate signal lines IT1 to ITn are coupled. Opening/closing of the discharge switch DC and the charge switch EC is controlled by control signals (CD and CE) output from the control unit 27C.

An operation of the A/D conversion circuit of FIG. 19 will be described using FIGS. 22, 23A, 23B, 24A, and 24B. As similar to the example, the switching control of the A/D conversion circuit differs depending on the input terminal (selected input channel) in which A/D conversion is performed and the input terminal (unselected input channel) in which A/D conversion is not performed. The input channels are the first input channel to the n-th input channel, but the n-th input channel will be described below as a representative channel.

When a signal of the input terminal CHn is A/D converted, the control unit 27C puts the input signal selection switch Fn in a conductive state, and puts the input signal selection switches other than the input signal selection switch Fn in a non-conductive state. In a period CD of FIG. 22, in order to suppress the influence of the electric charges when A/D conversion is performed at a different terminal before the electric charges of the signal generation source are charged to the S/H circuit unit C1, the control unit 27C puts the bypass switch GAn and the amplifier switch GBn in a non-conductive state, and puts the discharge switches D and DC in a conductive state before A/D conversion to discharge the electric charges from the S/H circuit unit C1 and the parasitic capacitance units 25A and 31 as shown in FIG. 24A. Namely, the control unit 27C puts the switches other than the discharge switches D and DC in a non-conductive state. A case in which the electric charges are discharged will be mainly described below. However, the same control is performed even in the case where the electric charges are charged. The period CD corresponds to the charging or discharging period of the S/H circuit unit C1 and the parasitic capacitance unit 31.

In a period A of FIG. 22, after the electric charges are discharged from the S/H circuit unit C1, the control unit 27C puts the amplifier switch GBn and the common switch I in a conductive state to charge the electric charges of the signal generation source to the S/H circuit unit C1 using an output from the common amplifier IB as shown in FIG. 23A. The control unit 27C puts each switch of the charge unit 21 and the discharge unit 28C and the bypass switch GAn in a non-conductive state.

In a period B of FIG. 22, in order to improve the accuracy of A/D conversion, the control unit 27C puts the amplifier switch GBn in a non-conductive state, and puts the bypass switch GAn in a conductive state to charge the electric charges of the signal generation source to the S/H circuit unit C1 as shown in FIG. 23B. The control unit 27C puts each switch of the charge unit 21C and the discharge unit 28C in a non-conductive state. The period A and the period B correspond to the sampling period of the S/H circuit unit C1 (period S). In a period C of FIG. 22, after the charging of the electric charges of the signal generation source to the S/H circuit unit C1 is completed, A/D conversion is performed by putting the bypass switch GAn in a non-conductive state. The period C corresponds to the conversion period of the A/D conversion unit 26.

A case in which a signal of the input terminal CHn is not A/D converted and the charging of the electric charges to the S/H circuit unit C1 is determined on the basis of the lower limit to detect disconnection will be described. The control unit 27C puts the input signal selection switch Fn in a non-conductive state, puts the bypass switch GAn, the amplifier switch GBn, and the common switch I in a non-conductive state, and puts the discharge control switch Nn in a conductive state to discharge the electric charges charged to the parasitic capacitance unit 23 in a period PCD of FIG. 22 as shown in FIG. 24B. The control unit 27C puts each switch of the charge unit 21C and the discharge switch D in a non-conductive state. The period PCD corresponds to the discharging or charging period of the input signal line FTn. When the input terminal CHn is in a disconnection state, the electric charges are discharged from the parasitic capacitance unit 23 to discharge the electric charges from the input signal line FTn to the A/D conversion unit 26 when A/D conversion is performed. Accordingly, the comparison determination unit 29 determines that the A/D conversion result becomes around 0V, and the disconnection state is detected.

A case in which a signal of the input terminal CHn is not A/D converted and the charging of the electric charges to the S/H circuit unit C1 is determined on the basis of the upper limit to detect disconnection will be described. The control unit 27C puts the bypass switch GAn, the amplifier switch GBn, and the common switch I in a non-conductive state, and puts the charge control switch Mn in a conductive state to charge the electric charges to the parasitic capacitance unit 23 in the period PCD of FIG. 22. The control unit 27C puts each switch of the discharge unit 28C and the charge switch E in a non-conductive state. When the input terminal CHn is in a disconnection state, the electric charges are charged to the parasitic capacitance unit 23 to charge the electric charges from the input signal line FTn to the A/D conversion unit 26 when A/D conversion is performed. Accordingly, the comparison determination unit 29 determines that the A/D conversion result becomes around a power supply voltage (for example, 5V), and the disconnection state is detected.

In each input channel, the period CD, the period A, the period B, and the period PCD are periodically repeated in order. The period CD, the period A, and the period B of one input channel are performed in parallel with the period PCD of a different input channel.

According to the third modified example, even in the circuit configuration in which the amplifier provided on a terminal basis is shared by a plurality of terminals, the electric charges can be discharged from the parasitic capacitance and the S/H circuit unit by the above-described additional circuit and the switching control or can be charged to the parasitic capacitance and the S/H circuit unit. Thus, disconnection can be detected during normal A/D conversion as similar to the first modified example, thereby leading to a contribution to downsizing of the chip size of the semiconductor device.

<First Application>

A configuration of a motor control system according to a first application will be described using FIG. 25. In the case where a three-phase motor 3 used for automobiles and industries is controlled by a microcontroller 1, the microcontroller 1 controls output values (a motor driving signal of a motor control timer 18 and an excitation waveform signal of an excitation signal generation timer 19) to the three-phase motor 3 according to a current value of each phase of the three-phase motor 3 from a driver/inverter/current detection circuit 2 and an output from a resolver 4. Because of the following reasons, the A/D conversion circuit 11B of the second modified example is used in the first application.

(1) In order to obtain the rotational angle and speed of the three-phase motor 3, the current value of each phase of the three-phase motor is sampled using a U-phase current value, a V-phase current value, and a W-phase current value from a current detection circuit 2. However, an output of the current of each phase is sequentially changed depending on time. It is necessary to simultaneously obtain the current value of each phase to accurately control the three-phase motor 3, and thus the terminal S/H circuit (S&H) is used.

(2) The resolver 4 is used to obtain the rotational angle of the three-phase motor 3. An excitation waveform signal is output from the excitation signal generation timer of the microcontroller 1 to the resolver 4, and analog values of a Sin waveform signal and a Cos waveform signal are output from the resolver 4 to the A/D conversion circuit 11B of the microcontroller 1. In order to detect the rotational angle on the basis of the phase difference between the Sin waveform signal and the Cos waveform signal from the resolver 4, the analog values need to be simultaneously held, and thus the terminal S/H circuit (S&H) is used.

<Second Application>

A configuration of an air-bag system according to a second application will be described using FIG. 26. An air-bag of an automobile determines a collision of the vehicle using the microcontroller 1 on the basis of signals from various sensors (a G sensor 7, a yaw rate sensor 8, and the like). The signals from the sensors are analog signals. Thus, when the signals are received by the microcontroller 1, the signals are converted to digital signals by the A/D conversion circuit 11. It is not necessary to simultaneously fetch the signals of various sensors in the second application. Thus, the A/D conversion circuits 11, 11A, and 11C of the example and the first and third modified examples are used.

The invention achieved by the inventors has been described above in detail on the basis of the embodiment, the example, and the applications. However, it is obvious that the present invention is not limited to the embodiment, the example, and the applications, but can be variously changed. 

What is claimed is:
 1. A semiconductor device comprising: a first input terminal configured to receive a first voltage; a second input terminal configured to receive a second input voltage; a signal transmission circuit that selects one of the first and second input terminals; an A/D conversion circuit that couples to the selected input terminal; and a comparison determination circuit that compares an output signal from the A/D conversion circuit with a first voltage and detects a disconnection of the second input terminal, wherein the second input terminal couples to the signal transmission circuit through a channel, wherein the second input voltage has a voltage range between a second voltage and a third voltage lower than the first voltage, the second voltage being lower than the first voltage; wherein when the signal transfer circuit selects the first input terminal, the channel is coupled to the first voltage, wherein when the signal transfer circuit selects the second input terminal after the selection of the first input terminal, the comparison determination circuit detects the disconnection upon a match result of the comparison.
 2. The semiconductor device according to claim 1, further comprising a central processing unit (CPU), wherein when the comparison determination circuit detects the disconnection, the comparison determination circuit outputs an interruption signal to the CPU.
 3. The semiconductor device according to claim 1, wherein the first voltage is a power supply voltage.
 4. A semiconductor device comprising: a first input terminal configured to receive a first voltage; a second input terminal configured to receive a second input voltage; a signal transmission circuit that selects one of the first and second input terminals; an A/D conversion circuit that couples to the selected input terminal; and a comparison determination circuit that compares an output signal from the A/D conversion circuit with a first voltage and detects a disconnection of the second input terminal, wherein the second input terminal couples to the signal transmission circuit through a channel, wherein the second input voltage has a voltage range between a second voltage and a third voltage lower than the first voltage, the third voltage being higher than the first voltage; wherein when the signal transfer circuit selects the first input terminal, the channel is coupled to the first voltage, wherein when the signal transfer circuit selects the second input terminal after the selection of the first input terminal, the comparison determination circuit detects the disconnection upon a match result of the comparison.
 5. The semiconductor device according to claim 4, further comprising a central processing unit (CPU), wherein when the comparison determination circuit detects the disconnection, the comparison determination circuit outputs an interruption signal to the CPU.
 6. The semiconductor device according to claim 4, wherein the first voltage is a ground voltage. 